Research Needs and Applications to Reduce Erosion and Sedimentation in Tropical Steeplands (Proceedings of the Fiji Symposium, June 1990): IAHS-AISH Publ. No.192,1990.
Soil erosion in East Kalimantan, Indonesia
T. STADTMUELLER Indonesian-German Forestry Project, Faculty of Forestry, Mulawarman University, Samarinda, Indonesia ABSTRACT In East Kalimantan, soil characteristics and the hilly topography favour soil erosion as soon as the vegetative cover is broken. In most areas, if soil conservation is not applied from the moment of opening new lands, erosion will occur and soil fertility will decrease. Large areas have already deteriorated towards unproductivity. The present paper discusses the main erosion-relevant issues, including logging, shifting cultivation, transmigration, forest fires, alang-alang grasslands, pepper plantations and coal mining. The establishment of environment and soil conservation programs is most necessary in East Kalimantan which has been seriously damaged by deforestation, fire, erosion and intrusion of alang-alang. The watershed management approach is strongly recommended for planning and execution of such programs. The fact that in East Kalimantan, the limits of districts and subdistricts in many cases coincide with basin divides is a great political and administrative advantage for such programs. INTRODUCTION Much of the interior of Indonesia's so-called outer islands is in many ways "terra incognita", because soil characteristics, climate and ecology have still to be explored. Kalimantan, the biggest of these outer islands was hoped to become an economic miracle through the exploitation of its petroleum and forest resources. East Kalimantan which has almost the size of the Federal Republic of Germany has also been considered one of the principle transmigration areas for people from overpopulated Java and Bali, even though only 6.6% of its total area is suitable for agriculture without major infrastructural investment (TAD-BAPPEDA, 1982). Research on erosion under virgin forests in East Kalimantan showed that weathering and erosion are in a dynamic equilibrium even though litter transport and overlandflow occur. However, if the thin but very protective litter cover is removed denudation rates increase sharply by rainsplash detachment (Besler, 1987). Environmental degradation including soil erosion, river siltation, water quality problems and loss or degradation of genetic material in East Kalimantan is evident but scarcely documented. The hilly topography with relatively steep slopes even in the lowlands, favours soil erosion as soon as the vegetative cover is broken. The principal factors and agents that cause accelerated erosion will be described and discussed in the following sections.
EROSION-RELEVANT ISSUES Logging Effects of mechanical logging on soil properties can be very profound, above all if logging is carried out with heavy equipment, as is common in forest concessions in the humid tropics. If logging is followed by fire, erosion is even greater (Ewel & Conde, 1980). The heavy machinery churns up and compacts the soil making it vulnerable to erosion. Skidder trails become rivers of mud a few minutes after rainstorms occur. Rivers draining logging areas soon become highly polluted (Chin, 1987). Among physical, chemical and microbiological soil properties, the former are most relevant for erosion. Physical effects on soils include compaction and loss of structure. Undisturbed forest soils tend to have higher values for crumb stability and porosity and lower values for bulk density than soils that have been cleared (Ewel & Conde, 1980). Hamzah (1978) reports data on bulk densities of different sites in a logged-over forest in East Kalimantan (Table 1 ) . He also took a few measurements on infiltration at field capacity on an untrafficked area, under a skyline and on a skidding road, resulting in 6.0, 0.26 and 0.0 mm/min respectively.
Table 1 Some bulk density...